Sunday, December 04, 2016

Tribblix and the new illumos loader

Recently, a new boot loader was added to illumos, which will in time replace the old and venerable grub that we've been using for about a decade.

I've been looking at how this will impact Tribblix.

The boot loader's arrival was heralded long in advance. I actually released Tribblix milestone 18 when I did to ensure I didn't have to deal with any loader issues. Not that I was expecting any issues, but just in case.

The first step in looking at the impact of the new loader was to build a current copy of illumos. I had a couple of issues due to recent illumos changes. The first being that the transition to Python 2.7 didn't work with my copy of python (I need to build a dual 32/64 bit installation) so I used the old copy of python 2.6. The second was that the loader wants /usr/sfw/bin/gstrip, which I've never had, but a quick symlink set that straight.

The loader is a new package. The first thing I tried was to build an ISO exactly as I always have. This ISO knows nothing about the new loader, doesn't have the loader present, and uses grub just as it always has. If you pretend the new loader doesn't exist, everything just works the way it did before. That's encouraging as a fallback position

Next step was to add the package for the new loader, and persuade the ISO to boot from it. This was very easy, you just need to change the path to the boot image when calling mkisofs. For grub, it was

-b boot/grub/stage2_eltorito

and for the new loader it becomes

-b boot/cdboot

That should be it, but it then tripped up on a Tribblix customization. The loader needs to know where the kernel and the boot archive are. The defaults are reasonable, but use $ISADIR to pick up a 32 or 64-bit image as required. On live media, Tribblix has a single merged boot archive, so I need to override the boot_archive_name to not use $ISADIR. So I create a file /boot/loader.conf.local that contains



and then make sure that I delete that file on the installed image, where things will look like a regular system again.

Thinking about this, it would have been more sensible to drop a file into /boot/conf.d which is another location that the loader uses for customization. I use this for something else, I create a file /boot/conf.d/chaindisk containing


and the loader menu will have a "boot from hard disk" entry, which I think you do need on media. Again, this gets deleted from the installed system where it doesn't make any sense.

Something else you can do is tweak the branding. I've played with changing the illumos name on the boot screen with Tribblix (look at the ascii art in /boot/forth/brand-illumos.4th for example).

To make the installed system bootable used to involve messing with installgrub, now bootadm can manage it for you. That's just

/sbin/bootadm install-bootloader -M -P rpool

and it should handle pools with multiple drives correctly.

The only other thing the installer needs to do, as far as I can tell, is initialize the list of boot environments. This is similar to grub, and involves putting 2 lines into /rpool/boot/menu.lst, for example

title Tribblix 0.19
bootfs rpool/ROOT/tribblix

and there you are. Some relatively simple changes and Tribblix is ready to use the new loader.

Well, almost. This needs to be packaged up and polished, and I still need to change and test the UFS installer, SPARC builds, and installation into an existing pool.

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